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what size would you do.

Got a call to install an evap. coil and a/c in a modular. Total square foot about 1300, 2 x 6 walls, minimal windows, new house. The factory installed a 4 ton blower in the a/h with 15 kw. There are a total of 6, count them SIX vents 2 1/4 by 12. Also r32 in attic. No adding new vents. Return is 20" flex.

Do a load calc, and advise whomever, what needs to be done to do the job properly. If they want it done otherwise, just make sure you get it in writing that they were advised.
Funny how some consumers can be so penny wise!

load calc is the best way to go, the only way to ensure how many btu's are required sounds like a 4 ton is a little large to me. depending on heat load calc i would roll with a 3 ton with 10 kw. not sure the area your in but there is a formula to determine HS kw..

There is no cookie-cutter answer when it comes to selecting equipment. Load calc....that's it.

Not meaning to sound critical, but......Is it just me, or is there a basic problem when a technician/business owner comes out here to ask fellow posters how to properly select equipment for a job?

This is certainly a good place to share ideas, experiences, etc. But if you're not capable of selecting/sizing/designing the proper equipment for a job and have to resort to assistance from an online group....might want to consider taking the necessary steps to ready yourself for this task.

Thank you for the friendly advice. LOAD calcs DO NOT answer all questions.
LOAD CALCS are not cookie cutter annswers. You have to see the bigger picture. I don't have time to explain all of the details.

I think the guys have a handle on the scenario.

I have six vents for a 4 ton blower with 5 x 15 duct. We are going to have pressure problems as we are not allowed to increase circulation..

We are going to have a heat transfer problem.

Last time I checked load calcs had something to do with ductwork.

But that is just me. 4 tons is way too big to cool this house.

But I guess, really, I was just frustrated and wanted to share my feelings, with the guys. I really didn't want their advice.

checked them. Thank you. The home owner is not open to new vents in her new floors.
No vents in three rooms, including the laundry ion the north end.

The factory should have done this right. This lady doesn't want the belly of her house cut open, to run new duct in a house that was supposed to be done right in the first place. The bathroom, dining room and laundry have no vents.

AC size

I'd be hesitant as well with out adding supplies and return. The way it stands I'd be at 1.5 tons with 2 ton evaporator and set fan to medium speed then see the pressures. Still not the best setup. I'd prefer a 2 ton with 4 more supplies. I think any larger with the good insulation you state would be too big.

Originally Posted by ironpit

Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

The heat isn't my problem. The a/h came with the home.

I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

The really annoying thing is this house was sold by my accountant.He sells modulars.

He originally asked me if I was interested in the duct work and furnace part of the job, but I was swamped so I told him no. Plus the job is about 60 miles away.I told him he would save a lot of money and time to have the factory do it. They would do it right. The factory was unbelievably cheap. I couldn't touch their price.

what size would you do.

Originally Posted by ironpit

Got a call to install an evap. coil and a/c in a modular. Total square foot about 1300, 2 x 6 walls, minimal windows, new house. The factory installed a 4 ton blower in the a/h with 15 kw. There are a total of 6, count them SIX vents 2 1/4 by 12. Also r32 in attic. No adding new vents. Return is 20" flex.

I would size it based on the Heat Load performed.

Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

The heat isn't my problem. The a/h came with the home.

I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

I was hired for a/c only.

Without a load calc; how would you know what "pressures" you even need?

Thank you for the friendly advice. LOAD calcs DO NOT answer all questions.
LOAD CALCS are not cookie cutter annswers. You have to see the bigger picture. I don't have time to explain all of the details.

I think the guys have a handle on the scenario.

I have six vents for a 4 ton blower with 5 x 15 duct. We are going to have pressure problems as we are not allowed to increase circulation..

We are going to have a heat transfer problem. Last time I checked load calcs had something to do with ductwork.

But that is just me. 4 tons is way too big to cool this house.

But I guess, really, I was just frustrated and wanted to share my feelings, with the guys. I really didn't want their advice.

You can't produced an answer without seeing the whole "picture", via a Load Calc.

checked them. Thank you. The home owner is not open to new vents in her new floors.
No vents in three rooms, including the laundry ion the north end.

The factory should have done this right. This lady doesn't want the belly of her house cut open, to run new duct in a house that was supposed to be done right in the first place. The bathroom, dining room and laundry have no vents.

This is one of those I can't believe it jobs.

Produce a Heat Load Calc and show the customer. Doesn't the IMC require it? If you do it your way; you're just guessing. Any way you wouldn't have any proof of evidence why your installs would be right without a Qualified document (Load Calc)!

I diidn't say I did not do a heat load calc, nor did I say it wasn't a proper thing to do.But at this point with a 4 ton blower on 5 x 15 duct with 6 vents I can see other problems.
For the record I did not do a load calc,as of yet. I will.

But I am stuck with this air handler and 6 vents. Is it just me or do I see problems?

I know the duct work is wrong. There are three rooms without vents and I've got a lady with a new house who isn't crazy about opening the belly of her house to install more ductwork on her new house.

Nobody is knocking a heatload calc.

I am trying to fit an a/c in a house that I know the ductwork is insufficient. I am trying to do it within the parameters I am given.

It isn't what I want to do, but I'm pretty much in the position of fitting the a/c to the duct instead of the duct to the a/c, as would normally be done with a load cal.